There is a constant search in the field of television for new effects which can be used to aesthetically enhance television pictures, either by improving their actual or perceived quality or by modifying the pictures for artistic reasons.
One method of improving picture quality is to apply a technique known as aperture correction to the video signals. Video signals are generated by scanning an image to take samples which have a finite size determined by the dimensions of the apparatus used. Aperture correction techniques seek to correct for the finite size of the samples, to create the video signal which would have resulted from a smaller, preferably infinitesimally small sample size. Aperture correction is used, for instance, in telecine apparatus.
A telecine is a known piece of equipment which is designed to product TELEvision signals from CINEmatographic film, and is commonly used by television stations and the like to provide television signals from feature films or from news material recorded on film.
There are basically three known types of telecine, namely flying spot, camera tube, and solid state array (usually linear array) telecines. In a flying spot telecine, the film runs between a cathode ray tube operating as a light source and a simple light-sensitive detector. The cathode ray tube is arranged to display a single spot of light which follows a raster such as to scan the film with the desired scan pattern, and the detector output thus forms the basis of a television signal. The less-common camera tube type is in a sense the converse of this, as the whole film frame is illuminated by a source, opposed to which is a camera tube which operates with an appropriate scanning raster but otherwise like any other television camera to provide a scanned output. So far as solid state array types are concerned, only linear array types are on the market and in these the film runs between a light source and a linear semiconductor light sensor arranged across the film path on the other side of the film. Typically the sensor will have 1024 individual elements or cells. Thus one line is sensed at a time, and the array is amptied as though it were a shift register to provide a signal representing one line. Two-dimensional arrays can be foreseen in which more than one line might be available simultaneously.
The size of the image samples used to generate the video signals are determined by the size of the scanning spot or the size of the sensor cells. Aperture correction is used to correct for these finite sizes. A correction signal is derived by sampling the video signal before and after a portion representing a detail to be enhanced, and the correction signal is then added to the original video signal at that portion. Correction is normally applied in both the horizontal and vertical directions, that is by sampling the picture to either side of the detail (horizontal correction) and above and below the detail (vertical correction).
It was an object of the invention to enable video signals from a telecine to be processed to create effects other than aperture correction, and to provide these effects in ways which permit of pre-programming by a system such as that described below and in the U.S. patent application referred to above.